CSE 113 Week 3 January 28 – February 1, 2008

Monday Announcements  Software Installation Fest: 2/5 and 2/6 4pm – 7pm in Baldy 21 Bring your laptop or desktop to have appropriate software installed!  Module 1 due 2/8  Module 2 due 2/15

Monday Game Plan  Exam 1  More work with objects

Monday  We can create a world  We can create a turtle and put it in the world  If we assign the turtles to a variable, then we can ask them to do things

Monday  Things turtles can do: moveTo(int, int) turnRight() turnLeft() forward() forward(int) turn(int) penUp() penDown()

Wednesday Announcements  Software Installation Fest: 2/5 and 2/6 4pm – 7pm in Baldy 21 Bring your laptop or desktop to have appropriate software installed!  Exam 2 on 2/6  Module 1 due 2/8  Module 2 due 2/15

Wednesday Game Plan  Vocabulary and terminology

Wednesday  It is important to know the proper terms for the things we are studying, so we should make sure we clarify the names of the programmatic elements you have been working with so far this semester.

Wednesday  new Turtle()  new is a keyword in Java. Keywords are special to the language and can only be used for a specific purpose. Java knows these purposes, so every time it sees that keyword it performs the exact same operations each time.  When it sees new, it knows we are about to create a new instance of something.

Wednesday  new Turtle()  Turtle is the name of the class we are creating an instance of, but in the context of this entire statement, Turtle is the name of a constructor that we are trying to invomke. Constructors for classes have the same name as the class itself.

Wednesday  new Turtle()  The () are called a parameter list. Parameter lists provide additional information to a constructor when we are calling it. Note that sometimes our parameter lists have been empty and other times we have needed to put information inside them.

Wednesday  new Turtle()  This whole line is used when we are creating an object.  We can create an object and assign it to a variable by using this code: Turtle t = new Turtle();

Wednesday  After we have a variable that refers to our object, we can call methods on it to ask the object to perform actions for us.  The syntax for a method call is: object.methodName();

Wednesday  object.methodName();  object is the name of the object (the name of the variable referring to the object) that we would like to invoke the method upon.  methodName is the name of the method we are trying to invoke  () is another parameter list, can be empty or have information.

Wednesday  In order for the object to be able to react to the method call, the method must have been pre-defined inside the code.  Note that some methods that have the same name (like forward in the Turtle) can exist together. The reason for this is because they take different parameters.

Wednesday  The grid the turtles live on is like the coordinate plan you may have studied in math class, but it has some key differences you should know about. The origin (0,0) is in the upper left hand corner. X-values increase going right Y-values increase as you go down

Friday Announcements  Software Installation Fest: 2/5 and 2/6 4pm – 7pm in Baldy 21 Bring your laptop or desktop to have appropriate software installed!  Exam 2 on 2/6  Module 1 due 2/8  Module 2 due 2/15

Friday Game Plan  Working with Media (not Turtles)  What happens when you reassign variables that are referring to Turtles?

Friday  There is a picture object that you can create.  It needs to know what the name of the file is that should be displayed.  You can get this by using the FileChooser.pickAFile() method.  There is a Sound object that can be created as well.

Friday  Variables that refer to Turtles and to other objects as well are slightly different than those that referred to numbers.  If you have two turtles t1 & t2 defined and you say:  t1 = t2;  Both t1 & t2 refer to the same turtle and the turtle that is referred to by t1 is no longer accessible in the program.